Here is a square sequence of numbers.

392?
6 3
7 4
?817

What are the two question marks?

Going in a clockwise direction, any given digit is obtained by adding the two preceding digits and reducing the sum to to mod 10. This gives the completed arrangement as:

3 9 2 1
6 3
7 4
9 8 1 7

Accordingly, the digits appearing at the two question marks are respectively 1 and 9**.**